1. Field of the Invention
The present invention relates to ion beam bending magnets and particularly such magnets adapted to accommodate and bend a ribbon-shaped ion beam having a cross-sectional profile with a major dimension normal to the bending plane of the magnet.
2. Background of the Invention
Magnets used for bending the path of an ion beam are known in various applications, especially in the field of ion implantation. One use of bending magnets in ion implantation is for filtering a beam of ions from an ion source, so as to produce a filtered beam comprising substantially only ions having a desired mass to charge ratio. As is well understood in this field, when a beam containing ions having a predetermined energy passes through a region of substantially homogenous magnetic field, transverse to the beam direction, the ions of the beam adopt curved paths having radii of curvature dependant on the mass charge ratio (m/q) of the individual ions. In this way, ions in the beam of differing m/q become spatially separated in a bending plane, so that unwanted ions can be filtered from the beam by passing the beam through a mass resolving slit. Mass analyzer magnets providing the required region of transverse homogenous magnetic field are well known in the field of ion implantation. In such mass analyzer magnets, the bending plane of the magnet is a plane normal to the direction of the homogeneous magnetic field.
It is also known, particularly in the field of ion implantation, to produce a ribbon-shaped ion beam having a cross-sectional profile which has a major dimension and a minor dimension. Ribbon-shaped ion beams may be used in ion implantation to provide a uniform implant dose over a substrate to be implanted, by providing relative scanning between the ribbon beam and the substrate in a single direction orthogonal to the major dimension of the ribbon beam. For this purpose, the major dimension of the ribbon beam at the implant location should extend right across the substrate. Known semi-conductor substrates for the fabrication of electronic devices comprise semi-conductor wafers with radii up to 300 mm.
Ion implantation is also used in the fabrication of flat panel displays, including for example LCD displays. In the case of the fabrication of flat panels for display devices, the panels to be implanted may have a transverse dimension of 800 mm or more. If such panels are to be implanted by means of a ribbon beam, then the major dimension of the ribbon beam needs to exceed the dimension of the panel to be implanted. It is important when implanting using a ribbon beam that the ribbon beam has excellent uniformity over the large dimension of the ribbon, so that substrate can be implanted uniformly by scanning the substrate through the ribbon beam transversely of the large dimension of the ribbon. This has led to implanters being manufactured in which a ribbon beam is extracted directly from the ion source and then transported to an implant station for implanting the desired substrate. Typically the ribbon-beam is passed through an analyzer magnet in order to select from the beam of ions extracted from the ion source substantially only ions of the desired mass required for implantation.
In the case of a ribbon beam, it is known to pass the ribbon beam through an analyzer magnet in which the magnetic field is directed parallel to the large dimension of the ribbon, with a view to bending the ribbon beam uniformly so that the required ions will pass through a mass resolving slit having the same long dimension as the major dimension of the ribbon beam. Providing a suitable uniform magnetic field over the full large dimension or width of the ribbon beam implies a magnetic pole spacing for the analyzer magnet which is sufficient to accommodate the large dimension of the ribbon beam. The resulting magnet can be extremely massive if the required magnetic field uniformity is to be obtained, both over the full gap of the magnetic poles, and for the required path length required to bend the ion beam to achieve a desired mass resolution. The difficulty of constructing a suitable analyzer magnet increases along with increases in the large dimension of the ribbon-beam to be analyzed.
Although the bending of a ribbon beam in a bending plane normal to the major dimension of the ribbon is discussed above in relation to mass analysis of the beam, ion beam bending magnets may be used for other purposes, including beam directional control, and beam scanning.